In the manufacture of printed wiring boards or other articles requiring electroless plating on a non-metallic substrate, a palladium colloidal catalyst is often employed to initiate the autocatalytic (electroless) plating on the substrate. Quite often, metal, e.g., copper, is present on the substrate when it is immersed in the catalytic bath. For example, when employing copper clad substrates which are drilled to provide through-holes, these through-holes must be metal plated to provide a continuous current path. Since the exposed surface in the hole is non-metallic, electroless plating techniques including the step of catalyzation by means of a tin/palladium colloidal catalyst is generally employed. Copper clad boards are immersed in the catalytic bath to deposit the catalyst thereon.
It has been found that with continued use, the catalytic bath becomes contaminated with copper from the copper cladding. When contamination reaches an extent such that the bath becomes ineffective or the electroless plating becomes less adherent than desirable, the bath is said to be "spent" and must then be discarded as waste.
Previously, such waste baths have been combined with other plant waste which are either discarded or treated for metal recovery.
It would be desirable, however, due to the relatively high value of palladium, to be able to effectively and relatively inexpensively recover the palladium from the spent catalytic baths in a form to allow it to be easily refined prior to its combination with other waste products.